The invention relates to an improved process for the preparation of 7-aryl-3,5-dialkoxy-4-alkyl-hepta-2,6-dienoic acid alkyl ester which comprises reacting the corresponding 3-aryl-propenal with a 3-oxo-alkanoic acid alkyl ester to afford a 7-aryl-3,5-dihydroxy-4-alkyl-hepta-2,6-dienoic acid alkyl ester which is then subsequently alkylated.
7-aryl-3,5-dialkoxy-4-alkyl-hepta-2,6-dienoic acid alkyl esters are useful as intermediates for the preparation of a variety of beta-methoxyacrylates which are useful as fungicides. In particular, they are key intermediates in the preparation of myxothiazole and oudemansins which are described, for example, in Martin et al., Tetrahedron Letters, 32, 5151, 1993.
7-aryl-3,5-dialkoxy-4-alkyl-hepta-2,6-dienoic acid alkyl esters are generally disclosed in WO 99/12892 but there is no specific disclosure of their preparation.
Martin et al., Tetrahedron Letters, 34, 32, 5151, 1993 disclose a method for the preparation of myxothiazole which comprises reacting 3-phenyl-propenal with 3-oxo-pentanoic acid methyl ester followed by three methylation steps to yield 7-phenyl-3,5-dimethoxy-4-alkyl-hepta-2,6-dienoic acid methyl ester as an intermediate for myxothiazole. This process requires many steps to achieve an overall yield of the desired 7-aryl-3,5-dialkoxy-4-methyl-hepta-2,6-dienoic acid alkyl ester of less than 20%.
The novel process of the present invention has been found to be advantageous in producing 7-aryl-3,5-dialkoxy-4-alkyl-hepta-2,6-dienoic acid alkyl esters with high overall yields in only one or two steps.
It is an object of the present invention to provide an efficient and improved process for the preparation of 7-aryl-3,5-dialkoxy-4-alkyl-hepta-2,6-dienoic acid alkyl esters of formula I.
Other objects and advantages of the present invention will be apparent to those skilled in the art from the following description and the appended claims.